1. Field of the Invention
The present invention relates to a silicon-containing compound; a method for surface treatment of an electrode, using the silicon-containing compound; a surface-treating agent of an electrode, comprising the silicon-containing compound; and an organic electroluminescence device obtained by treating an anode with the silicon-containing compound.
2. Related Art of the Invention
Recently, many studies on electronic or photoelectronic devices using organic materials have intensively been made. However, few devices are composed only of the organic material and, in almost all of cases, a device structure is formed by laminating the organic material and inorganic material. Since such an electronic or photoelectronic device consists of many inorganic/organic interfaces, because it has a structure fabricated by laminating the organic material over the inorganic material in the device, it is important to control of the mechanical and electric characteristics of the interface to improve the device performance.
In an organic electroluminescence device, for example, an inorganic transparent conductive electrode of indium-tin oxide (hereinafter abbreviated to ITO, sometimes), tin oxide (SnO2), zinc oxide (ZnO), etc. is often used as a transparent conductive electrode for transmitting light and injecting holes. The device is constructed by forming a layer of an organic hole transporting material on this transparent conductive electrode, but the interface between the transparent conductive electrode and the organic hole transporting material has the following problem. That is, an ITO electrode, SnO2 electrode or ZnO electrode is used after washing the surface according to solvent washing, plasma washing, etc. and the hydroxyl group or alkoxy group is formed on the surface of the surface-washed ITO electrode, SnO2 electrode or ZnO electrode, thereby hydrophilizing the electrode. Since a hydrophobic functional organic material is generally used as a hole transporting film to be formed on the transparent conductive electrode, peeling of the film arises sometimes because of poor adhesion at the interface. No problem arises when a hydrophilic functional organic molecule is further formed on this hydrophilic conductive electrode. For example, Japanese Patent Kokai Publication No. 2-267888 discloses an organic electroluminescence device obtained by forming a polysilane thin film having the hole transporting property on an ITO electrode. Since a conventional polysilane compound has only a hydrophobic group on the side chain, satisfactory adhesion is still to be obtained, necessarily.
A surface-treating agent represented by a silane coupling agent is widely used as a modifier of the interface between composite materials prepared by using organic materials in combination with inorganic materials, such as elastomer, paint, adhesives, sealant, resin coat, etc., including fiber-reinforced plastic. It becomes possible to improve the adhesion between the inorganic layer and organic layer by treating with this surface-treating agent. Since almost all of surface-treating agent, which have hitherto been used, have no electron transporting property or hole transporting property, it serves only as an electric insulator, thereby to drastically deteriorate performance as the electronic or photoelectronic device.
On the other hand, the work function of the ITO electrode, SnO2 electrode or ZnO electrode hardly agrees with the ionization potential of the organic hole transporting material, and a difference in potential between the transparent conductive electrode and organic hole transporting material arises. This difference in potential becomes an potential barrier to holes in case of injecting holes from the transparent conductive electrode into the organic hole transporting material, sometimes. This potential barrier causes reduction in probability of injection of holes from the transparent conductive electrode to the organic hole transporting material, thereby lowering the injection efficiency of holes. In order to solve this problem, an attempt of vacuum deposition of metal phthalocyanine having an intermediate ionization potential between the work function of the transparent conductive electrode and the ionization potential of the organic hole transporting material in the semitransparent state has been made. However, it is pointed out that the light transmission is lowered because the metal phthalocyanine has absorption in the visible light region.
An object of the present invention is to provide a novel silicon-containing compound; a method for surface treatment of an electrode, using the silicon-containing compound wherein the mechanical/electric contact between an electrode (e.g. transparent conductive electrode, etc.) and an organic layer is improved; an surface-treating agent of an electrode, comprising the silicon-containing compound; and an organic electroluminescence device (hereinafter referred to as an xe2x80x9corganic EL devicexe2x80x9d, sometimes) having excellent mechanical and electric contact between an electrode and an organic layer, which is obtained by treating an anode with the silicon-containing compound.
The present inventors have intensively studied about a surface-treating agent having the hole transporting property so as to solve the above mechanical and electric problems of the conventional technique. As a result, the present inventors have found that the injection efficiency of holes into the organic layer and adhesion can be improved by treating the surface of the electrode with a specific silicon-containing compound. Thus, the present invention has been accomplished.
The present invention relates to [1] a silicon-containing compound having an oxidation potential of 0.3 to 1.5 V on the basis of a standard hydrogen electrode, wherein at least one alkoxy group is bonded to a silicon atom and at least one aromatic amine group is also bonded to the silicon atom.
Furthermore, the present invention relates to [2] the silicon-containing compound according to the term [1], wherein a structural formula is represented by the general formula (1): 
wherein R1 represents a hydrogen atom, or a straight-chain or branched alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 10 carbon atoms or less, an aryl group having 6 to 24 carbon atoms or an aralkyl group having 7 to 26 carbon atoms; R2 represents a straight-chain or branched alkyl group having 1 to 10 carbon atoms; R3 represents a straight-chain or branched alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 10 carbon atoms or less, an aryl group having 6 to 24 carbon atoms or an aralkyl group having 7 to 26 carbon atoms; Ar1 represents an arylene group having 6 to 24 carbon atoms; Ar2 represents a straight-chain or branched alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 10 carbon atoms or less, an aryl group having 6 to 24 carbon atoms or an aralkyl group having 7 to 26 carbon atoms, or the general formula (2): 
wherein Ar3 represents an arylene group having 6 to 24 carbon atoms; and R4 and R5 independently represent a straight-chain or branched alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 10 carbon atoms or less, an aryl group having 6 to 24 carbon atoms or an aralkyl group having 7 to 26 carbon atoms; s and t independently represent an integer from 1 to 3, which satisfy the expression 2xe2x89xa6s+txe2x89xa64; and a ring may be independently formed between R3 and Ar1, R3 and Ar2, or Ar1 and Ar2, or alternatively a ring may be independently formed between R4 and Ar3, or R4 and R5 when Ar2 is represented by the general formula (2).
Also, the present invention relates to [3] a method for surface treatment of an electrode in a device having an organic layer in contact with the electrode, which comprises treating the surface of the electrode with the silicon-containing compound of the term [1] or [2] or a silicon-containing compound which has an oxidation potential of 0.3 to 1.5 V on the basis of a standard hydrogen electrode and is represented by the following general formula (3): 
wherein R1, R2, s and t are the same as those defined in the general formula (1); and A represents a condensed polycyclic aromatic group having 14 to 30 carbon atoms.
Also, the present invention relates to [4] a surface-treating agent of an electrode, comprising the silicon-containing compound of the above term [1] or [2] or the silicon-containing compound represented by the general formula (3) of the term [3].
Also, the present invention relates to [5] an organic electroluminescence device comprising a pair of electrodes of an anode and a cathode, at least one of which is transparent or semitransparent, and at least one organic layer formed between the electrodes, wherein the anode is treated with the silicon-containing compound of the term [1] or [2] or the silicon-containing compound represented by the general formula (3) of the term [3].